Engine (steam locomotive)
The engine of a steam locomotive refers to the entirety of the drive elements . This essentially includes
The drive mechanism and boiler do not belong to the engine .
Steam locomotives were built with two-, three- and four-cylinder engines, both with single-stage expansion and with compound effect , in which the high-pressure steam initially works on cylinders with a small diameter (high-pressure cylinder) and the exhaust steam with its residual pressure works on a large cylinder (low-pressure cylinder).
In the simple case, a steam locomotive has two engines, the right and the left, both of which act on cranks on the same axle. Occasionally, a third or even a fourth engine is added, which act on a cranked axle in the middle between the wheels of the vehicle . Often the cranked crank axis of the central engines is not the same axis as that of the external engines.
Machines are known from the USA in which tender axles are also driven by separate engines.
Locomotives with multiple bogies have more than two engines (articulated locomotive types, e.g. Mallet or Garratt ).
Special designs of engines for steam locomotives are on the one hand compact steam engines and on the other hand steam turbine drives, which were experimented with in the 1930s without lasting success. Only the cardan shaft type Shay with its steam engines in V-arrangement prevailed for the operation of forest railways , especially in America .